1. Field of the Invention
The present invention concerns a method and a device for coil selection of a magnetic resonance apparatus and in particular for coil selection of a magnetic resonance apparatus in which the patient support device is moved continuously through the magnetic resonance apparatus during an examination of a subject.
2. Description of the Prior Art
In addition to a whole-body acquisition coil (also known as a body coil) that is permanently installed behind the tunnel cowling in a magnetic resonance apparatus, modern magnetic resonance apparatuses also have a number of local acquisition coils (also known as local coils). In an imaging examination with the magnetic resonance apparatus, the local coils deliver a measurement signal with significantly better signal-to-noise ratio than the whole-body acquisition coil, since the local coils can be placed directly on or optimally close to the body of the patient or the subject to be examined. Moreover, the signals of the local coils are less significantly disrupted by other system components of the magnetic resonance apparatus.
However, the use and the increasing number of the employed local coils and their placement along the body of the patient or the subject to be examined require an ever-greater time expenditure on the part of the technician for planning the examination. After the positions of the local coils have been determined relative to the patient, or relating to a support device on which the patient lies (such as by using a method disclosed in, for example, DE 10 2004 022 559 for determination of the position of a local coil), a subset of the employed local coils is selected such that the local coils define an acquisition region which encompasses the region to be examined (also called the field of view (FoV). The acquisition region of the coils is limited on the one hand by the homogeneity region of the magnetic resonance system and by regions of increased resolution which are bounded by the acquisition regions of the local coils. The homogeneity region can be, for example, a spherical volume of, for example, 50 cm in diameter within the magnetic resonance system.
During the measurement of a volume to be examined, the use of all arranged local coils can lead to additional noise signals or even interference signals from the local coils that are unsuitable for this region, and thus the image quality of the examination result is degraded. Moreover, magnetic resonance apparatuses typically have only a limited number of acquisition channels to which the local coils can be connected. A limitation of the selected local coils is thus also necessary for this reason.
The problem of the suitable coil selection is particularly important in measurements with continuous table movement, known as continuous table movement measurements or CTM measurements. Under the circumstances a very large examination region (which is also called a virtual large field of view (virtual large FoV)) that can be composed of a number of the aforementioned FoVs, is traversed during the continuous table movement. This can, for example, pertain to the entire body of the patient and thus exhibit a length of over 200 cm.